1. Field
The present disclosure relates generally to measurement devices and, in particular, to a method and apparatus for mounting a measurement device to an object. Still more particularly, the present disclosure relates to a method and apparatus for mounting a laser tracker in thermal isolation from an object to which the laser tracker is mounted.
2. Background
When manufacturing parts, it may be desirable to measure the physical characteristics of the part. These measurements may be made to determine whether the measurements are within tolerances or allowed thresholds for the part. These types of measurements may be made to perform quality control and to determine whether adjustments may be needed to the manufacturing process.
A coordinate measuring machine may be a device that may be used to measure physical characteristics of a part. This type of machine may be manually controlled and/or computer controlled. Measurements may be defined by a probe attached to a moving axis of the machine. This probe may collect information about various points on the surface of the part.
A coordinate measuring machine may have three axes that may be orthogonal to each other in a three-dimensional coordinate system. Each of these axes may have an extremely accurate scale system to indicate the location of the axes. The different measurements may be used to identify a size and position of the points.
One type of coordinate measuring machine may be a laser tracker. A laser tracker may use a laser beam that may be projected against the surface of the object. With a laser tracker, many points may be taken and used to check the size and position of a part. Further, these points also may be used to create a three-dimensional image of the part.
A laser tracker may be placed on an object, such as a tripod, a tool, a table, or some other suitable mounting object. A laser tracker may require a period of time to warm up. This warm-up time may be needed to avoid a drift and/or error in measurements. The warm up may be for electronics within the laser tracker. For example, the laser tracker may operate at a temperature range from around 75 degrees to around 80 degrees.
The warm up also may be needed to ensure that measurements do not vary. For example, if the housing in a laser tracker is made of aluminum, as the temperature increases, the size of the aluminum base may change in dimensions. This change may result in measurements that may vary. Drifting of measurements may be undesirable because these drifts may affect accuracy.
When a laser tracker is placed on a tool, the tool may have a temperature lower than the operating temperature of the laser tracker, such as, for example, around 65 degrees Fahrenheit. The temperature gradient between the operating temperature for the laser tracker and the temperature of the tool may cause heat to be transferred from the laser tracker to the tool until a thermal equilibrium occurs. In other words, the tool may act as a heat sink. While this temperature gradient is present, a drift in measurements may occur. The amount of time needed to warm up a laser tracker placed on a tool may be around 20 to around 36 hours.
The amount of time needed to warm up a laser tracker may increase the time needed to manufacture parts. This increase in time may delay manufacturing of parts until measurements can be made. Further, if parts are manufactured during the warm-up time and measurements later show that the parts may be out of tolerance, then those parts may need to be discarded and/or reworked.
Accordingly, there is a need for a method and apparatus that takes into account one or more of the issues discussed above, as well as possibly other issues.